1. Field of the Invention
The present invention relates to a gas leakage testing method which is used to detect a gas micro-leakage from a testing specimen in a gas leakage test.
2. Prior Art
Conventionally, there are provided several kinds of gas leakage testing methods and devices as shown in FIGS. 1 to 5.
FIG. 1 shows one of the conventional gas leakage testing devices which is designed according to the so-called vacuum method (i.e., the testing method in which probe gas is blown toward the testing specimen). Herein, a leakage detector 2 is connected to a testing specimen 1 such that gas can be flown between them. In addition, a suction pump 3 is connected to the testing specimen 1 so that the interior wall of the testing specimen 1 is subjected to evacuation. Further, there is provided a helium gas bomb which blows out helium gas (i.e., He gas) toward the outer wall of the testing specimen from its He-gas blowing pipe 5.
After subjecting the testing specimen to evacuation by use of the vacuum pump 3, this device interconnects the leakage detector 2 to the inside of the testing specimen, so that He gas is blown toward the testing specimen 1 via the blowing pipe 5. If a leakage point exists in the wall of the testing specimen 1, He gas must be introduced into the testing specimen 1 from such point, which is detected by the leakage detector 2.
FIG. 2 shows another device according to another vacuum method (i.e., hood-type testing method which also blows the probe gas toward the testing specimen). Herein, in a manner similar to the foregoing device shown in FIG. 1, the testing specimen 1 can be selectively connected to one of the leakage detector 2 and suction pump 3. Further, this testing specimen 1 is covered by a container such as a hood 6.
In this device, the .vacuum pump 3 subjects the testing specimen 1 to evacuation, and then helium gas is filled in the hood 6. In this state, if a leakage point exists in the testing specimen 1, He gas is introduced into the leakage detector 2 via this point, so that the leakage detector 2 will detect He-gas leakage. According to this device, it is possible to detect the gas leakage in the whole portion of the testing specimen 1, by which gas leakage quantity can be measured as a whole.
FIG. 3 shows a gas leakage testing device according to the vacuum internal-pressure method. Herein, the testing specimen 1 which is filled with He gas in advance is inserted into a chamber 7, and then the vacuum pump 3 subjects this chamber 7 to evacuation. In this state, if a leakage point exists in the testing specimen 1, He gas must be leaking from this point, which is detected by the leakage detector 2.
FIG. 4 shows a gas leakage testing device according to the sniffer method. Herein, the testing specimen 1 which is filled with pressurized He gas is inserted into the chamber 7, and then the vacuum pump 3 subjects the chamber 7 to evacuation. In addition, a sniffer probe 9 sniffs around the testing specimen 1, and consequently, He gas leaking from the leakage point of the testing specimen 1 is detected by the leakage detector 2.
FIG. 5 shows a gas leakage testing device according to the integration method. Herein, the testing specimen 1 which is filled with pressurized He gas is inserted into a hood 8 the capacity of which is known. After the vacuum pump 3 subjects the hood 8 to evacuation, the testing specimen 1 is left as it is for a long time. In such period of time, this device measures variation of helium density in He gas to be leaked from the testing specimen 1. By integrating such variation of helium density, it is possible to detect a micro-leakage quantity.
Regardless of the above-mentioned features, each of the conventional gas leakage testing devices suffers from the following drawbacks.
In the devices as shown in FIGS. 1, 2, after subjecting the testing specimen 1 to evacuation, He gas is filled around the testing specimen 1, so that gas leakage is detected by detecting He gas to be introduced into the specimen 1. On the other hand, in the devices as shown in FIGS. 3 to 5, after filling the testing specimen 1 with pressurized He gas, gas leakage is detected by detecting He gas to be leaked to the outside of the specimen 1. As described above, the conventional devices subject the inside or outside (i.e., inside of the chamber) of the testing specimen 1 to vacuum evacuation. However, due to the existence of natural He gas (at 5 volppm) in the air, it is hard for the leakage detector to correctly detect the gas micro-leakage.
In order to detect such gas micro-leakage with accuracy, evacuation must be made to the highly vacuumed state, which makes the testing time longer. In addition, such highly vacuumed state may require more than two kinds of pumps to be coupled together, which makes the evacuation system more complicated.
When examining large number of testing specimens, vacuum evacuation must be made in a relatively short period of time. For this reason, it is necessary to provide a large-scale vacuum evacuation device, however, which raises the whole system cost higher.
Even if such large-scale vacuum evacuation device is used, volatile matter or water content may be produced from the testing specimen or wall of a testing container, and gas or air may be ejected from micro-holes of the testing specimen. Thus, it is hard to raise the degree of vacuum in a short period of time. In addition, He gas existing in the air may work as the background noise for the detector. These factors make the detecting precision for leaked He gas lower.